1. Field of the Invention
The invention relates generally to the field of photography, and in particular to a camera which when loaded with a lighttight film cartridge warns the user of a film take-up malfunction.
2. Description of the Prior Art
To load most 35 mm cameras, the film cartridge is inserted in a loading chamber of the camera and the forward end portion of a film leader projecting from a light trapping slit in the cartridge is placed over a film take-up spool in a take-up chamber of the camera. In some cameras, the forward end portion of the film leader is manually attached to the take-up spool before a back door of the camera is closed. Then, an initial film winding operation is performed, for example, by pivoting a winding lever and depressing a shutter release button several times until the entire leader is wound onto the take-up spool and the first available frame of the filmstrip is positioned for exposure. In other cameras, the forward end portion of the film leader is automatically secured to the take-up spool at the beginning of the initial film winding operation. As the take-up spool is rotated by a motor drive, for example, one or more circumferential teeth on the spool engage the forward end portion of the film leader in its perforations to wind the leader onto the spool and to position the first available frame of the filmstrip for exposure. A spring-like deflector or other suitable means may be provided on the back door of the camera for pressing the film leader against the take-up spool to facilitate engagement of the forward end portion of the leader by the teeth on the spool. After the first available frame of the filmstrip is exposed, subsequent exposures are made by repeating the film winding and shutter releasing operations.
A problem that exists in some 35 mm cameras as a consequence of the loading procedure is that, even though the user believes the forward end portion of the film leader is secured to the take-up spool, the forward end portion may fail to be engaged with the spool or may disengage from the spool during the initial film winding operation. As a result, the film leader will not be wound onto the take-up spool and the first available frame of the filmstrip cannot be positioned for exposure. However, since the back door of the camera is closed, the user may not become aware of the film take-up malfunction because the winding lever and the shutter release button can be manually operated in the usual way. The user, thus, under the delusion that the camera is working properly might begin photographing and would learn of the malfunction only when the back door of the camera is re-opened to remove the cartridge from the camera.
A prior art solution to the problem is disclosed in commonly assigned U.S. Pat. No. 4,334,753, issued Jun. 15, 1982. In this patent, when a film cartridge is first loaded into a 35 mm camera, a sensing lever is pivoted by a longitudinal edge of a reduced width leading section of the filmstrip to an intermediate position in which it blocks operation of a shutter release button and simultaneously provides a visual indication of the blockage in the viewfinder. If the leading section of the filmstrip is securely attached to a take-up spool in the camera and is wound at least partly onto the take-up spool in response to winding rotation of the spool, the sensing lever will be pivoted by a forward inclined edge of a full width main section of the filmstrip, following the leading section, from the intermediate position to another position in which it no longer blocks operation of the shutter release button and is removed from the viewfinder.